26 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 15, 



while they separated those which are really analogous, and probably 

 due to one and the same cause. 



I have already alluded, p. 12, to one most remarkable feature in 

 the structure of this district, that the crystalline rocks are most 

 massive where their foliation is vertical, and become more and more 

 schistose as its dip recedes from the perpendicular. This was well 

 described by Saussure, § ^11 ^ &c., and has struck every observer 

 who has followed him. This structure is the reverse of what occurs 

 in the Highlands of Scotland, where I pointed out that the foliation 

 is usually least marked where the angles of inclination are slight, and 

 most complete where the gneiss is perpendicular or hi2;hly inclined*. 

 Nor is this structure universal in Switzerland : it holds good in the 

 chains of the Aiguilles Rouges, Mont Blanc, the Finsteraarhorn, the 

 St. Gothard, Mont Combin, and the Dent Blanche ; in which there 

 is also a strong mineral resemblance, all partially consisting of proto- 

 gine. But the contrary structure is found in the great range of 

 crystalline rocks which extend from Monte Rosa through the canton 

 of Ticino : there, as in Scotland, the centres of the arches of foliation 

 consist of rock as compact as, and frequently more so than their flanks. 



This difference of structure produces a corresponding difference in 

 the physical features of the two great chains of the Alps : around 

 Mont Blanc and the Bernese Alps the axes of foliation and cleavage 

 run along deep and narrow valleys, and the harder rock, having its 

 divisional planes vertical, or nearly so, stands out in sharp peaks or 

 Aiguilles, often bounded by mural precipices ; in the southern range 

 from Monte Rosa to the Lago Maggiore, the central arches of folia- 

 tion are broad and elevated, constituting a large part of the chain, 

 which has no longitudinal valleys of importance on the line of the 

 strike of the foliation, and the mountains are usually more striking 

 from their massive grandeur than from the elegance of their outline. 

 But I will not now pursue this subject further, as I hope to have 

 opportunities of following it more effectually in future. 



Should any geologists be disposed to test in the country here 

 described the accuracy of the observations relating to cleavage and 

 foliation contained in this memoir, or to follow out the same subject 

 in other districts, let them recollect that there are everywhere minor 

 local irregularities arising from various disturbing agencies, which 

 must be overlooked, lest in overwhelming themselves with details, 

 they lose the power of obtaining general views of phaenomena which 

 extend over many hundred miles : Saussure, who was a minute 

 observer where minuteness was required, but who knew when to 

 dispense with it, has left us the following warning, " ce n'est pas avec 

 des microscopes qu'il faut observer les montagnes," § 1882. 



* Philosophical Transactions, 1852, p. 447. 



